Climate control systems for automotive vehicles require low weight, high pressure refrigerant compressors with a relatively high volumetric efficiency. It is known compressor design practice to use a rotary orbiting piston that cooperates with a compression chamber in a compressor housing.
The rotary piston of such a compressor design rotates about an axis that is offset from the axis of the compressor cavity. As the surface of the orbiting ring piston contacts the surface of the cavity of the housing, a pumping chamber of variable volume is established. The piston cooperates with inlet and outlet ports to distribute high pressure refrigerant to an expansion valve located between the compressor and the evaporator in the climate control system. During the portion of the compression cycle in which the working pressure chamber defined by the piston and the compressor cavity is expanding in volume, the refrigerant enters the cavity. Compressor vanes extend in a generally radial direction and engage the surface of the rotary piston to effectively seal the expanding portion of the working chamber from the compression portion of the working chamber.
The improvements of our invention can be used in either a single stage rotary compressor or a double stage rotary compressor, an example of the latter being disclosed in U.S. Pat. No. 5,284,426, which is assigned to the assignee of the present invention.
The rotary piston of the compressor shown in the '426 patent includes an orbiting piston that cooperates with the compression chamber and an internal cylindrical post. This defines multiple first-stage compression chambers and multiple second-stage compression chambers. The output of the first-stage supplies the inlet of the second-stage. The orbiting ring piston, which surrounds the post of the housing wall, rotates about an axis that is offset from the axis of the post as the outer surface of the piston contacts the inner surface of the housing and the inner surface of the orbiting ring piston contacts the outer surface of the post.
There are two sets of vanes; i.e., two external vanes and two inner vanes. The external vanes, which are slidably mounted in the housing, engage the outer surface of the orbiting ring piston, thereby defining two discrete first-stage compression chambers. The inner vanes, slidably mounted in the post, engage the inner surface of the orbiting ring piston, thereby defining two discrete second-stage compression chambers.
The two compression chambers for each stage are divided and are dynamically sealed, one with respect to the other, at the tangent contact points between the piston and the housing and between the piston and the post.